1. Field of the Invention
The present invention relates to an electric power supply control apparatus capable of executing an interruption process in case an electric power supply voltage is lower than a predetermined voltage, thereby achieving a self resetting.
2. Related Background Art
Mobile devices such as a camera generally have various electronic control system, and control means such as a microcomputer is often employed in a circuit constituting such electronic control system. Also the mobile devices such as a camera usually employ a battery as a power supply, and an electric power supply voltage elevated by an electric power supply circuit such as a voltage booster circuit is supplied to control means.
Such control means has, among operation modes, a high-speed operation mode of executing a predetermined high-speed operation with a high-speed clock signal of about 1 MHz to 100 MHz when an instantaneous operation, such as an image taking operation of a camera, is required. Such mode is capable of a high-speed operation but cannot be executed constantly because of a high current consumption. For this reason, in case of a control operation not requiring a high speed such as an update operation of a clock, if the camera is not operated, the control mode is shifted to a low-speed operation mode of operating the control means with a clock signal of less than 100 KHz, thereby suppressing the current consumption.
Thus, in the mobile device such as a camera, the control means usually has a high-speed operation mode and a low-speed operation mode.
Also in case the mobile device such as a camera is accidentally dropped, the internal battery may be instantaneously disconnected to cause a voltage drop, and, in such situation, the voltage booster circuit cannot maintain a constant voltage and also the electric power supply voltage for the control means becomes lower than a minimum operation voltage, whereby the control means becomes incapable of control.
In order to avoid such situation, a detection circuit for detecting the electric power supply voltage to the control means is externally provided with an output thereof being connected directly to a reset circuit of the control means to execute a direct hardware resetting or directly to an interruption port of the control means to execute a self resetting by a software, thereby preventing an uncontrollable situation.
However, in case the electric power supply voltage shows an instantaneous large change as spike noise for example due to an electrostatic charge, there may result a signal to be outputted into the electric power supply voltage detecting circuit even when the actual electric power supply voltage is not lower than the minimum operation voltage of the control means, or an interruption signal is generated into the control means even if the power supply voltage detecting circuit does not generate an output, thereby causing a hardware resetting or a self resetting of the control means by the software.
In case of such resetting, there may result a situation where the apparatus, which has been operating without any problem, returns to an initial state. As an example, in case a camera is reset by an electrostatic charge during a stand-by state, the date and time and various photographing data are reset to an initial state and the setting operation therefor has to be repeated again.
Also in case a resetting to an initial state occurs during a camera operation, for example during a zoom operation, the zoom operation is suspended in the course thereof to result in an extremely cumbersome situation. When such situation occurs frequently, the image taking operation itself is hindered.
On the other hand, in case the resetting is inhibited in order to avoid such situation, the control becomes impossible when the electric power supply voltage for the control means is actually lowered for example by a chattering of the battery of the mobile device.